Comparative microbial diversity and redox environments of black shale and stromatolite facies in the Mesoproterozoic Xiamaling Formation

Spatial and temporal trends in Precambrian nitrogen cycling: A Mesoproterozoic offshore nitrate minimum

“…We note that our results for the deep subtidal/basinal facies of the Bangemall and Roper groups (+1.8‰ ± 1.6‰, n = 28; +2.0‰ ± 0.8‰, n = 8 respectively) are in good agreement with basinal mudstones from the roughly contemporaneous Xiamaling Formation (δ 15 N bulk = +2.1±0.2‰, n = 4, age 1.37 Ga) (Luo et al, 2015). The facies-dependent trend in the Bangemall and Roper basins likely reflects primary nitrogen cycling rather than postdepositional alteration (see above), and so is interpreted as being consistent with cross-basin differences in nitrogen speciation, comparable to the Belt basin (Table 2; Stüeken, 2013).…”

“…Samples from hydrothermal cherts and amphibolite facies were excluded. Ader et al (2014) and Kikumoto et al (2014); (B) Mesoproterozoic era (1.6-1.0 Ga) with data from Stüeken (2013), Luo et al (2015) and this study; (C) Paleoproterozoic era (2.5-1.6 Ga) with data from Busigny et al (2013), Kump et al (2011) and Godfrey et al (2013). Subsets of the datasets listed above were taken to only include offshore environments: from Ader et al (2014) the Camil, Carmelo, and Copacel sections from Brazil and all data from Svalbard and North Canada.…”

“…From the Bangemall and Roper of this study, "deep" and "basinal" data respectively. From Luo et al (2015) all data. From Busigny et al (2013) data from the Brockman Iron Formation.…”

Paleoproterozoic sterol biosynthesis and the rise of oxygen

“…The derived steroidal and hopanoid hydrocarbons have similar thermodynamic stabilities and their concentrations in sedimentary rocks and petroleum decrease similarly as thermal maturity increases (Farrimond et al, 1998;Peters et al, 2005;van Graas, 1990). Yet the majority of Paleoproterozoic and Mesoproterozoic sedimentary rocks described that are known to preserve biomarkers appear to be devoid of eukaryotic steranes, but do contain C 27 -C 35 hopane hydrocarbons of bacterial origin (Blumenberg et al, 2012;Brocks et al, 2005;Flannery and George, 2014;Luo et al, 2015). From a micro-and macrofossil perspective, ample evidence exists for the presence of unambiguously eukaryotic fossil assemblages in the Mesoproterozoic (Butterfield, 2000;Javaux et al, 2001;Javaux et al, 2004;Knoll et al, 2006;Zhu et al, 2016).…”

“…Saturated sterane biomarkers typical of those found in Phanerozoic rocks were close to, or below, the methodological detection limits of ~1 p.p.m. Other biomarker studies of Archean, Paleoproterozoic and Mesoproterozoic sedimentary rocks, conducted in the era of heightened contamination awareness, reveal a similar picture of non-detection of eukaryote-specific 24-alkylated steranes (Blumenberg et al, 2012;Flannery and George, 2014;Hoshino et al, 2015) or their detection at levels than cannot be reliably distinguished from contamination (Luo et al, 2015;Zhang et al, 2016). Finally, new methodologies for evaluating the thermal regime experienced by sedimentary organic matter (Ferralis et al, 2016), the cleaning of contaminated rock samples prior to analysis (Jarrett et al, 2013) and a focus on directed identification and sampling of pockets of well-preserved Proterozoic and Archean sediments (Bruisten et al, 2013) suggest that the pre-Cambrian biomarker record can be elaborated and imbued with greater confidence.…”